Stabilization of a Reactive Cationic Species by Supramolecular Encapsulation Coordination Number Incommensurate Cluster Formation, Part 15. This research was supported by NSF grant CHE-9709621. We gratefully acknowledge Prof. Julie A. Leary and Dr. Ulla Andersen for their assistance with mass spectrometry. We also thank the Miller Foundation for a postdoctoral fellowship to M.Z. and the NIH for a postdoctoral fellowship to J.L.B. Part 14: J. Xide, K. N. Raymond, Angew. Chem. 2000, 112, 2857-2859; Angew. Chem. Int. Ed. 2000, 39, 2745-2747.